This invention relates to the transformer art, and it has particular relationship to transformers whose cores are composed of laminations of amorphous magnetizable material of small thickness. Typically, the thickness of the laminations is about 0.001-inch. This invention is uniquely advantageous for transformers whose cores are composed of wound webs of small thickness of amorphous magnetizable material and is disclosed herein in detail as applied to such transformers and cores. It is to be understood however, that the adaptation of the principles of this invention to transformers and cores composed of magnetizable materials of other types, for example, highly grain-oriented silicon iron, is within the scope of equivalents of this application and of any patent which may issue on, or as a result thereof, typically as scope of equivalents is applied in Grover Tank & Mfg. Co. v. Linde Air Products Co., 339 US 605; 70 Supreme Court Reporter 854 (1950) and interpreted in Uniroyal v. Rudkin-Wiley Corp., 5 USPQ 2d 1434 (CAFC 1988).
This invention concerns itself with transformers which are assembled with preformed coils which are telescoped on the legs of the core. To assemble such a transformer, it is necessary that the core, after being wound, be severed in a region and opened, to permit the telescoping of the coils, and thereafter reclosed. There are air gaps in the core of the completed transformer in the regions where the core is severed, increasing the magnetic reluctance which it is desirable to minimize.
U.S. Pat. No. 4,761,630, Frank H. Grimes and Eugenius S. Hammack, discloses a core with step-lap-butt joints in the regions of the cuts. In Grimes, the cuts are in staggered groups, each group including a plurality of peripherally offset steps which penetrate progressively inwardly into the core. In FIG. 3 of Grimes the steps are cut into the spiral, i.e., in the direction in which the spiral forming the core is wound, and the turn which bounds the inner end of an outer step and the outer end of the immediately adjacent inner step is overlapped. In FIG. 4 of Grimes the steps are cut out of the spiral, i.e., opposite to the direction in which the spiral is wound, and the overlap is between the last turn (8 or 7) of an outer step and the first separate turn (1) of the immediately adjacent inner step. There is also an overlap between the turn (7) which bounds the inner end of the last step of an outer group and the immediately adjacent inner step of an inner group. Effective reduction in reluctance was achieved in transformers embodying the Grimes invention. However, it is desirable to reduce the reluctance still further and it is an object of this invention to achieve this purpose.
In addition to Grimes, U.S. Pat. No. 4,741,096 Lee-Ballard is typical of the prior art. Lee discloses a transformer whose core is formed by winding a strip of ferromagnetic material on a first cylindrical mandrel, into an annulus, producing a radial cut through the annulus in one region, opening the annulus, winding the opened structure on a second mandrel having a diameter smaller than the first mandrel, and rearranging the laminations into what Lee calls "groups" which Lee says forms "packets" so that the "groups" overlap. Lee's teaching suffers the disadvantage that the cost of embodying it in a transformer is high. The rearrangement of the laminations on the second mandrel into "groups" and "packets" to produce the overlaps involves substantial cost. An important cost-factor is the necessity of counting the laminations of small thickness to subdivide them into "groups" and "packets" in rearranging the structure. In addition, it is desirable that the number of "groups" in Lee's "packet" be increased as the packets progress from the window of the core to its outer periphery. This involves the costly process of counting "groups" to effectuate the desired increase.
It is an object of this invention to overcome the disadvantages and drawbacks of prior art as taught by references such as Lee and to provide a relatively low-cost method of making a transformer having a core whose laminations or turns are overlapped to reduce magnetic reluctance. It is also an object of this invention to provide a method for providing a product for use in making a core for the transformer, made by the low-cost method.